The invention pertains to methods of forming sputtering targets, and further encompasses the targets formed by the methods.
A sputtering method is described with reference to FIG. 1, which illustrates a sputtering target 10 spaced from a substrate 12 by a distance T/S. Distance TIS is referred to as the target substrate distance. Substrate 12 can comprise, for example, a semiconductive material wafer. Target 10 can comprise numerous materials known to persons of ordinary skill in the art, such as, for example, metallic materials (e.g. one or more of aluminum, copper, titanium, tantalum, tungsten, cobalt, nickel, etc.), or ceramic materials (e.g., BaTiO3, Pb(Zr, Ti)O3, BiSrTaO3, etc.). Also, target 10 can comprise numerous shapes. For instance, FIG. 2 illustrates that target 10 can comprise a circular shape
Referring again to FIG. 1, a shield 14 is provided over a peripheral region of target 10. Shield 14 can comprise, for example, stainless steel or aluminum.
In operation, material from target 10 is sputter-deposited onto substrate 12. More specifically, target 10 has a face surface 16 which is exposed to high energy ions and/or atoms. The high energy ions and/or atoms eject atoms from surface 16, and the ejected atoms are subsequently deposited onto substrate 12. Shield 14 protects peripheral edges of target 16 from being exposed to the high energy ions and/or atoms. One of the goals in target fabrication is to deposit a uniform film of material over substrate 12. One aspect of achieving a uniform film is to have an appropriate T/S distance between target surface 16 and substrate 12, as well as to maintain a substantially common T/S distance from the entirety of the sputtered target face 16 and substrate 12. Shield 14 is provided to alleviate problems which could occur if the sloped regions of target 10 were exposed to high energy ions and/or atoms during a sputtering process.
FIG. 3 illustrates target 10 after the target has been subjected to the wear of having material sputtered therefrom. Specifically, FIG. 3 illustrates a wear profile formed across sputtered face surface 16. The illustrated wear profile is for exemplary purpose only. The shape of an actual wear profile can depend on, for example, the magnet type and target life of materials used in a sputtering process. A dashed line 18 is provided in FIG. 3 to illustrate the starting position of the face surface when target 10 was new (i.e., the face surface shown in FIG. 1). As shown in FIG. 3, a number of troughs (i.e., sputter tracks) are formed within face surface 16 during the sputtering operation. Accordingly, the target does not wear uniformly across the surface 16.
Attempts have been made to improve target lifetime by adding additional material to a target to compensate for the uneven wear pattern of FIG. 3. For instance, FIG. 4 illustrates a target 20 which attempts to compensate for the uneven wear of FIG. 3. Target 20 is shown with a dashed line 18 illustrating the position of original face 16 in the target 10 of FIGS. 1-3. FIG. 4 also shows additional material 22 provided over original position 18, and in locations which compensate for the uneven wear profile of FIG. 3. Accordingly, target 20 has a face surface 24 which effectively comprises a mirror image of the wear profile of FIG. 3.
FIG. 4 is one embodiment of prior art processes for compensating for the uneven wear profile of FIG. 3. Another embodiment is to simply form additional material 22 over various regions of 18, without necessarily creating a mirror image of the wear of FIG. 3. Regardless of which of the prior art techniques is utilized, the result is a target having relatively large peaks at positions in which wear has been most significant in prior targets. A difficulty with the processing of FIG. 4 is that target 20 has large variations in thickness across its surface, and accordingly a T/S distance relative to face 24 of target 20 varies significantly across the face. Accordingly, the uniformity of:film deposition from target 20 can be significantly less than the uniformity of film deposition from a target having a planar face. Thus, even though lifetime can be improved utilizing the target 20 of FIG. 4 instead of the target 10 of FIGS. 1-3, the loss in uniformity can render target 20 less desirable than previous targets 10 of FIGS. 1-3.
It would be desirable to develop techniques for forming targets having improved lifetimes, and which can be utilized to uniformly sputter-deposit materials on substrates.
In one aspect, the invention encompasses a method of forming a sputtering target. A wear profile for a sputtering target surface is determined. The wear profile corresponds to a shape of the target surface after the target is subjected to the wear of having material sputtered therefrom. It can be preferred to determine a wear profile from a target which has been exposed to an anticipated semiconductor wafer fabrication process (specifically, an anticipated sputtering process), for a maximum anticipated lifetime of the target. The maximum anticipated lifetime can vary depending on, for example, the sputtering chamber configuration, the target composition, and the target configuration. The wear profile is divided amongst a plurality of datapoints across the target surface. A difference in height of the target surface after the wear relative to a height of the target surface prior to the wear is calculated. The difference in height calculations generate a plurality of wear definition datapoints. Target lifetime datapoints are calculated using the wear definition datapoints, and sputtering uniformity datapoints are also calculated using the wear definition datapoints. A difference between the target lifetime datapoints and sputtering uniformity datapoints is calculated. A constant corresponding to the difference between a target lifetime datapoint and a sputtering uniformity datapoint is added to the sputtering uniformity datapoints to generate a desired profile for a sputtering target sputtering surface. A sputtering target is formed having a sputtering surface with the desired profile.
The invention encompasses another method of forming a sputtering target. A wear profile for a sputtering target surface is determined. The wear profile is divided amongst a plurality of datapoints to generate datapoints {S1 . . . Si}, where xe2x80x9cixe2x80x9d is a positive integer. Also, datapoints are generated to define the target surface prior to the wear, with the datapoints being {R1 . . . Ri}. Difference datapoints {A1 . . . Ai} are generated, with each datapoint An being defined as Rnxe2x88x92Sn. Target lifetime datapoints {B1 . . . Bi} are calculated. Each datapoint Bn is defined as ((An* y)+Q); where y is a constant greater than 0, and Q is a constant which can be 0. Sputtering uniformity datapoints {C1 . . . Ci} are calculated, with each datapoint Cn being defined as ((An*z)+P); where z is a constant greater than 0 and less than y, and where P is a constant which can be 0. Difference datapoints {D1 . . . Di} are calculated, with each difference datapoint Dn, being defined as (Bnxe2x88x92Ce). The difference datapoint having the greatest magnitude is determined, and is defined as Dmax. A desired profile dataset {E1 . . . Ei} is generated, with each datapoint En being defined as (Cn+Dmax). A sputtering target is formed to have a sputtering surface with a profile corresponding to the desired profile dataset.